[LLVMdev] Updating PHI for Instruction Domination?

[Ryan Taylor]

I guess not since Value is a superclass of Instruction.

On Mon, Feb 6, 2012 at 10:36 AM, Ryan Taylor <ryta1203 at gmail.com> wrote:

>
>
> ---------- Forwarded message ----------
> From: Ryan Taylor <ryta1203 at gmail.com>
> Date: Mon, Feb 6, 2012 at 10:36 AM
> Subject: Re: [LLVMdev] Updating PHI for Instruction Domination?
> To: Eric Christopher <echristo at apple.com>
>
>
> Since I'm not sure which instructions I might want to replicate, would it
> be possible to cast the Value from "PHINode::getIncomingValue" to
> "Instruction" and then copy that and cast it back?
>
>
> On Sun, Feb 5, 2012 at 8:49 PM, Ryan Taylor <ryta1203 at gmail.com> wrote:
>
>>
>>
>> On Sun, Feb 5, 2012 at 5:15 PM, Eric Christopher <echristo at apple.com>wrote:
>>
>>>
>>> On Feb 2, 2012, at 5:13 PM, Ryan Taylor wrote:
>>>
>>> > So my best bet is to try and work in reg2mem mode and then go back to
>>> mem2reg?
>>> >
>>>
>>> I wouldn't. That sounds painful.
>>>
>>> > I'm curious, it seems though when you split a block that the phis get
>>> updated, right?
>>>
>>> Sure. There's code in splitBasicBlock to do this. It should just take a
>>> little bit of work to get what you want done.
>>>
>>> -eric
>>>
>>
>> Yes, the first DOES sound painful (I want to avoid it) and the second is
>> not an option. I'm adding a second path in a loop.
>>
>> The old path: BB1->BB2/BB3, BB2->BB1/BB3, BB3->n/a
>>
>> The new path: BB1->H/BB2, BB2->F/K, H->F, K->F,  F->BB1/G, G->BB3
>>
>> There are PHI nodes in BB1 that come in from BB2 for values defined in
>> BB2. With the new possible path: BB1->H->F, BB2. Without adding new PHIs or
>> Values, there exists a dominance instruction issue. So I want to create
>> PHIs in F for each value in BB2 that is used in BB1. The update the PHI
>> Values in BB1 (that used to come from BB2) to the new values in F (which
>> are getting values from BB2/H).
>>
>> The problem is that there is no way to copy the value from BB2, since
>> there exists no Value constructor!?
>>
>> This seems like a pretty large limitation anytime anyone wants to add a
>> branch inside a loop? Is there an easier way to get what I want that I'm
>> missing?
>>
>
>
>
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